If p cos A = 2q sin A and 2p cosec A - q sec A = 3, then the value of p2 + 4q2 is:
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Correct answer: B
Explanation
The correct answer is Option 2 i.e. 4.
⇒ p cos A = 2q sin A and 2p cosec A - q sec A = 3
⇒ p cos A = 2q sin A
Dividing both sides by cos A
⇒ p = 2a sin A/cos A
⇒ p = 2q tan A.....(1)
Now,
⇒ 2p cosec A - q sec A = 3
Put eq 1
⇒ 2(2q tan A) cosec A - q sec A = 3
⇒ 4q tan A cosec A - q sec A = 3
⇒ Since, cosec A = 1/sin A, sec A = 1/cos A, and tan A = sin A/cos A
⇒ 4q tan A cosec A - q sec A = 3
⇒ 4q × sin A/cos A × 1/sin A - q × 1/cos A = 3
⇒ 4q × 1/cos A - q × 1/cos A = 3
⇒ (4q - q)/cos A = 3
⇒ 3q/cos A = 3
⇒ q = cos A
Putting in eq 1
Then, p = 2 sin A
Now, Using sin2 A + cos2 A = 1
⇒ p2 = (2 sin A)2 = 4 sin2 A
⇒ 4q2 = 4(cos A)2 = 4 cos2 A
Thus,
⇒ p2 + 4q2 = 4sin2 A + 4cos2 A
⇒ 4(cos2 A + sin2 A) = 4
Hence, the value of p2 + 4q2 is 4