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🔑 Show Answer Key — Set 1
- 1. Slope of the join = 8/(−8) = −1, so the perpendicular slope is 1. (B) 1 .
- 2. $$ x^4+16x^2+64=(x^2+8)^2 $$ Answer $$ \boxed{(2)\ 16x^2} $$ <div
- 3. (D) None of these. Explanation: f(x+y)=x+y+1/2, f(x)+f(y)=x+y+1, and f(x)·f(y)=(x+1/2)(y+1/2)=xy+½(x+y)+1/4. None of the equalities/inequalities hold for all x,y (for example x=1,y=1 gives f(2)=2.5, f(1)+f(1)=3, f(1)·f(1)=2.25).
- 4. (i) Common ratio: $$ \frac93=\frac{27}9=\frac{81}{27}=3 $$ Answer G.P. (ii) Ratios are not equal. Answer Not a G.P. (iii) Common ratio: $$ \frac{0.05}{0.5}=0.1 $$ Answer G.P. (iv) Common ratio: $$ \frac12 $$ Answer G.P. (v) Common ratio: $$ -5 $$ Answer G.P. (vi) Ratios are not equal. Answer Not a G.P. (vii) Common ratio: $$ \frac14 $$ Answer G.P.
- 5. $$ \boxed{(2)\ (ii)\ \text{and}\ (iii)\ \text{only}} $$ <div
- 6. Area = ½ × base × height = ½ × 10 × 5 = 25. (B) 25 sq.units .
- 7. x = 60(cot30° − cot45°) = 60(√3 − 1) ≈ 60(0.732) = 43.92 m. (B) 43.92 m .
- 8. tan(elevation) = height/shadow = √3, so the angle = 60°. (D) 60° .
- 9. Collinear ⇒ equal slopes: (p − 7)/(3 − 5) = (6 − 7)/(6 − 5) ⇒ (p − 7)/(−2) = −1 ⇒ p = 9. (C) 9 .
- 10. The distance from the Y-axis stays constant at 10, so the path is the vertical line (A) x = 10 .
- 11. 1/(1 + tan²θ) = 1/sec²θ = cos²θ, so the value = sin²θ + cos²θ = 1. (B) 1 .
- 12. 25x² − 25/y² = (5x)² − (5/y)² = sec²θ − tan²θ = 1. (B) 1 .
- 13. (i) R1 = {(2,1),(7,1)} — Not a relation, since 1 ∉ B. (ii) R2 = {(-1,1)} — Not a relation, since -1 ∉ A (and 1 ∉ B). (iii) R3 = {(2,-1),(7,7),(1,3)} — This is a relation: all first elements are in A and all second elements are in B. (iv) R4 = {(7,-1),(0,3),(3,3),(0,7)} — Not a relation, since 0 ∉ A.
- 14. You must show both pairs of opposite sides are parallel — i.e. the slopes of two pairs of opposite sides. (B) .
- 15. tan²θ = x²/a² and sec²θ = y²/b². Since sec²θ − tan²θ = 1, we get y²/b² − x²/a² = 1. (A) y²/b² − x²/a² = 1 .
- 16. > Note: > The original rational expression was incomplete in the provided OCR/source text. > Full numerator and denominator were not visible. General Method If $$ A-B=C $$ then $$ B=A-C $$ So, the rational expression to be subtracted can be found by: 1. Taking LCM of denominators 2. Simplifying 3. Subtracting appropriately
- 17. $$ l^2=r^2+h^2 $$ $$ 13^2=5^2+h^2 $$ $$ 169=25+h^2 $$ $$ h^2=144 $$ $$ h=12 $$ Answer $$ \boxed{(1)\ 12\text{ cm}} $$
- 18. (f(x)-5)/x = (2x+5-5)/x = (2x)/x = 2, for x ≠ 0. Answer: 2 (with x ≠ 0).
- 19. $$ \angle AOB=180^\circ-\angle APB $$ $$ =180^\circ-70^\circ $$ $$ =110^\circ $$ Answer $$ \boxed{(2)\ 110^\circ} $$ <div
- 20. Let the common radius be r and height = 2r. Cylinder: V1 = πr²(2r) = 2πr³. Cone: V2 = (1/3)πr²(2r) = (2/3)πr³. Sphere: V3 = (4/3)πr³. Ratio V1:V2:V3 = 2 : 2/3 : 4/3 = 6:2:4 = 3:1:2.
- 21. Area required: $$ 10^2+11^2+\dots+24^2 $$ $$ = \sum_{1}^{24}n^2 - \sum_{1}^{9}n^2 $$ $$ = \frac{24(25)(49)}{6} - \frac{9(10)(19)}{6} $$ $$ =4900-285 $$ $$ =4615 $$ Answer $$ \boxed{4615\text{ cm}^2} $$
- 22. A×C = {(1,5), (1,6), (2,5), (2,6)}. Each first component (1 or 2) belongs to B and each second component (5 or 6) belongs to D, so every pair of A×C is also in B×D. Therefore A×C ⊆ B×D.
- 23. Subtracting a constant from every observation does not change standard deviation. Answer $$ 4.5 $$
- 24. Suppose $$ f(a)=f(b) $$ Then, $$ 2a-1=2b-1 $$ $$ 2a=2b $$ $$ a=b $$ Hence $f$ is one-one. The range is $$ \{1,3,5,7,\dots\} $$ Even natural numbers are not images of any element. Hence the function is not onto.
- 25. $$ \boxed{ (A^T)^T=A } $$ Verified.
- 26. Using Pythagoras theorem: $$ d^2 = 18^2 + 24^2 $$ $$ =324+576 $$ $$ =900 $$ $$ d=\sqrt{900} $$ $$ d=30 $$ Answer $$ \boxed{30\text{ m}} $$
- 27. Let external radius $R$, internal radius $r$ $$ R+r=14 $$ Width: $$ R-r=4 $$ Using identity: $$ R^2-r^2=(R+r)(R-r) $$ $$ =14\times4 $$ $$ =56 $$ Volume: $$ V=\pi h(R^2-r^2) $$ $$ =\pi(20)(56) $$ $$ =1120\pi $$ Answer $$ \boxed{1120\pi\text{ cm}^3} $$
- 28. Compute A × C = {(1,5), (1,6), (2,5), (2,6)}. Since every first component (1 or 2) belongs to B and every second component (5 or 6) belongs to D, each ordered pair of A × C is also an element of B × D. Hence A × C ⊆ B × D.
- 29. $$ \boxed{(3)\ \angle B=\angle D} $$ <div
- 30. (i) Inclination θ = tan⁻¹(0) = 0° . (ii) Inclination θ = tan⁻¹(1) = 45° .
- 31. Number of letters in 8th set: $$ 4^8 $$ Cost per letter: $$ ₹2 $$ Total cost: $$ 2\times4^8 $$ $$ =2\times65536 $$ $$ =131072 $$ Answer $$ \boxed{₹131072} $$
- 32. $$ \boxed{(2)\ \text{Two}} $$ <div
- 33. Given: $BC=5.6\text{ cm}$ $\angle A=40^\circ$ Angle bisector meets BC at D such that $CD=4\text{ cm}$ Construction Steps 1. Draw BC. 2. Mark D on BC such that $CD=4\text{ cm}$. 3. Using angle bisector theorem locate A. 4. Join AB and AC. Required triangle obtained.
- 34. Let S = 1 + 2 + … + k. Then 1^3+…+k^3 = S^2 = 44100, so S = √44100 = 210. Answer: 210
- 35. Let the intercepts be a and b: a + b = 1, ab = −6 ⇒ a, b are roots of t² − t − 6 = 0 ⇒ (t − 3)(t + 2) = 0 ⇒ {3, −2}. Intercept form x/a + y/b = 1 gives: x/3 + y/(−2) = 1 ⇒ 2x − 3y − 6 = 0 , and x/(−2) + y/3 = 1 ⇒ 3x − 2y + 6 = 0 .
- 36. Prove that the ratio of their volumes is $3\sqrt3:4$. Proof Let radius of sphere be $R$. Let radius of hemisphere be $r$. Surface area of sphere: $$ 4\pi R^2 $$ Total surface area of hemisphere: $$ 3\pi r^2 $$ Given equal: $$ 4\pi R^2=3\pi r^2 $$ $$ R^2=\frac34r^2 $$ $$ R=\frac{\sqrt3}{2}r $$ Volume of sphere: $$ V_1=\frac43\pi R^3 $$ Volume of hemisphere: $$ V_2=\frac23\pi r^3 $$ Ratio: $$ V_1:V_2 = \frac43\pi R^3:\frac23\pi r^3 $$ $$ =2R^3:r^3 $$ Substitute: $$ R=\frac{\sqrt3}{2}r $$ $$ =2\left(\frac{\sqrt3}{2}\right)^3 $$ $$ =\frac{3\sqrt3}{4} $$ Hence, $$ 3\sqrt3:4 $$ Hence proved.
- 37. Solving 8x + 3y = 18 and 4x + 5y = 9: 2(4x + 5y) − (8x + 3y) = 18 − 18 ⇒ 7y = 0 ⇒ y = 0, then x = 9/4. Intersection (9/4, 0). Midpoint of (5, −4) and (−7, 6) = (−1, 1). The required line passes through (9/4, 0) and (−1, 1). Slope = (1 − 0)/(−1 − 9/4) = 1/(−13/4) = −4/13. Through (9/4, 0): y = (−4/13)(x − 9/4) ⇒ 13y = −4x + 9. Therefore 4x + 13y − 9 = 0 .
- 38. (i) Each term is multiplied by 3. $$ 72\times3=216 $$ $$ 216\times3=648 $$ $$ 648\times3=1944 $$ Answer $$ 216,\ 648,\ 1944 $$ (ii) Common difference: $$ 1-5=-4 $$ $$ -3-1=-4 $$ Continue subtracting 4. Answer $$ -7,\ -11,\ -15 $$ (iii) Pattern: $$ \frac{1}{2^2},\frac{2}{3^2},\frac{3}{4^2} $$ Thus next terms are: $$ \frac4{5^2},\frac5{6^2},\frac6{7^2} $$ Answer $$ \frac4{25},\ \frac5{36},\ \frac6{49} $$
- 39. Construction outline: Draw base PQ of required length 6.8 cm. At the midpoint (or the chosen vertex for the vertical angle), construct the vertical angle of 50°. From the vertex, draw the angle bisector and mark point D on the base such that PD = 5.2 cm. Using these constraints, locate the third vertex so that the bisector meets the base at D. Join vertices to complete ΔPQR. Note: steps summarise the standard ruler-and-compass approach; precise drawing requires graphical construction on paper.
- 40. Points are collinear when the area of the triangle they form is 0. (i) ½|(−1/2)(6 − 8) + (−5)(8 − 3) + (−8)(3 − 6)| = ½|1 − 25 + 24| = 0 ⇒ collinear . (ii) ½|a((c+a) − (a+b)) + b((a+b) − (b+c)) + c((b+c) − (c+a))| = ½|a(c−b) + b(a−c) + c(b−a)| = 0 ⇒ collinear .
- 41. Let temperatures be: $$ a-2d,\ a-d,\ a,\ a+d,\ a+2d $$ First condition: $$ (a-2d)+(a-d)+a=0 $$ $$ 3a-3d=0 $$ $$ a=d $$ Second condition: $$ a+(a+d)+(a+2d)=18 $$ $$ 3a+3d=18 $$ Since $a=d$, $$ 6a=18 $$ $$ a=3 $$ Thus: $$ -3^\circ C,\ 0^\circ C,\ 3^\circ C,\ 6^\circ C,\ 9^\circ C $$ Answer $$ -3^\circ C,\ 0^\circ C,\ 3^\circ C,\ 6^\circ C,\ 9^\circ C $$