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If a2 + a = 13, then find the value of (a + 4)3 – 1/(a + 4)3
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The correct answer is option 1 i.e. 364.
a2 + a = 13
a2 + 8a + 16 = 7a + 13 + 16
(a + 4)2 - 1 = 7 (a + 4)
(a + 4) – 1/(a + 4) = 7
(a + 4)3 – 1/(a + 4)3 = 7 (72 + 3) = 7 × 52 = 364
If sin A+ sin2 A = 1, then the value of cos4 A + cos6 A is:
The correct answer is option 2 i.e. sin A.
Given that
If sin A+ sin2 A = 1,
sin A = 1 - sin2 A = cos2 A
the value of cos4 A + cos6 A
⇒ cos4 A + cos6 A
⇒ (cos2 A)2 + (cos2 A)3
⇒ sin2 A + sin3 A
⇒ sin A (sin A + sin2 A)
⇒ sin A × 1
⇒ sin A
If the median and mean are 36 and 35 respectively, find the mode.
The correct answer is option 2 i.e. 38.
median = 36
Mean = 35
Mode = 3(Median) - 2(Mean)
Mode = 3(36) - 2(35)
⇒ Mode = 108 - 70
⇒ Mode = 38
If a - b = 10 and ab = 4, then the value of a3 - b3 + 4(a + b)2 is:
The correct answer is Option 3 i.e. 1584.
(a + b)2 = (a - b)2 + 4ab = 102 + 4 × 4 = 116
a3 - b3 + 4(a + b)2
= (a - b)[(a - b)2 + 3ab] + 4(a + b)2
= 10 × (100 + 12) + 4 × 116
= 1120 + 464
= 1584
The circumcentre of a ΔABC is O. If ∠ BAC = 70° and ∠ BCA = 80°, then the measure of ∠ OAC is equal to:
The correct answer is Option 3 i.e. 60°.
∠ABC = 180° - (70° + 80°) = 30°
∠BOC = 2 × ∠BAC = 140° (central angle theorem)
In ΔBOC (isosceles), ∠OBC = ∠OCB = 20°
∠OCA = 80° - 20° = 60°
In ΔOAC (isosceles), ∠OAC = ∠OCA = 60°
A vertical pole and a vertical tower are on the same level ground in such a way that, from the top of the pole, the angle of elevation of the top of the tower is 60º and the angle of depression of the bottom of the tower is 30º. If the height of the pole is 24m, then find the height of the tower (in m).
The correct answer is option 4 i.e. 96.
Two pillars A and B of the same height are on opposite sides of a road which is 40 m wide. The angles of elevation of the tops of the pillars A and B are 30º and 45º, respectively, at a point on the road between the pillars. What is the difference (in m) of the point from the foot of pillar A?
In the given figure, AD is the angle bisector of ∠CAE, CD = 6 cm, and DE = 8cm. Find the length of BC.
The correct answer is Option 1 i.e. 18.
From figure ∠BAD = ∠BDA
⇒ AB = BC
AB = BD = x (let)
By the tangent secant property
⇒ BA2 = BC × BE
⇒ x2 = (x - 6)(x + 8)
⇒ x2 = x2 + 2x - 48
⇒ x = 24
⇒ BC = x - 6 = 24 - 6 = 18 cm
The resistance of a wire is proportional to its length and inversely proportional to the square of its radius. Two wires of the same material have the resistance 2:3 and their radii are in the ratio 8: 7 . If the first wire is 128 cm. Find the length of the other wire?
The correct answer is option 2 i.e. 147 cm.
Let the radius of a wire = r
length of a wire = l
R ∝ l / r2
R1 / R2 = l1 / l2 × (r2 / r1)2
2/ 3 = 128 / l2 ( 49 / 64 )
l2 = 147 cm
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