Question

if sinA = 4/5 find the value of 3cosA – 4 cos³A
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Answer 1

Answer:

sinA=opposite side/hypotenuse=4/5

so,

O.S=4

HYP=5

according to Pythagoras theorem,adjacent side is 3

now

tanA=O.S/A.S=4/3

cosA=A.S/HYP=3/5

secA=5/3

cotA=3/4

substituting the values,

= {(4×(4/3)}-{5×(3/4)} / {5/3+(4×(3/4))}

= {(16/3)-(15/4)} / {(5/3)+(12/4)}

= { (64-45)/12} / { (20+36)/12 }

= (19/12) / (56/12)

ans:

Explanation: