Trig Q: cos(a)=4/5, a in QIV; sin(b)=5/13, b in Q1. Find cos(2b), cos(a + pi/2).

[91powerramman]

Hi, I'm working on a final review packet for my trg class and can't figure where to even start with this question.

Given cos (alpha)= 4/5 with alpha located in quadrent IV, and sin(beta)=5/13 with beta located in quadrent I.
Find: cos(2Beta), and cos(alpha+pi/2)

Any help would be greatly appreciated, thanks

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[Deleted member 4993]

Hi, I'm working on a final review packet for my trg class and can't figure where to even start with this question.

Given cos (alpha)= 4/5 with alpha located in quadrent IV, and sin(beta)=5/13 with beta located in quadrent I.
Find: cos(2Beta), and cos(alpha+pi/2)

Any help would be greatly appreciated, thanks

Sent from my SM-T800 using Tapatalk

cos (alpha)= 4/5 with alpha located in quadrant IV → sin(α) ≤ 0 = - √[1-(4/5)² = -3/5

Similarly

sin(beta)=5/13 with beta located in quadrant I → cos(ß) ≥ 0 = √[1-(5/13)² = 12/13

now continue.....