Question

If sin theta = - 4/5 and pi < theta< 3pi/2, then cos theta/2 is equal to
(a) root 2/5 (b) -root 2/5 (c) 1/ root 5 (d) -1/root 5

Answer 1

Answer:

$➜\sf\red{Answer:-}$

this might be easier to handle if you think in degrees.

pi/5 radians = 36º and

3pi/10 rad = 54º

did you notice that they add up to 90º and did you know that the cos (any angle) = sin (90 -any angle) ?

so cos(36º)= sin(54º) = (1+√5)/4

BTW, cos 36º is exactly half the Golden Ratio, which would bring me to the Fibonacci numbers and other most fascination topics that I could spend hours ......

$➜\sf\red{hope \: this \: will \: help \: u:-}$

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Answer 2

this might be easier to handle if you think in degrees.

this might be easier to handle if you think in degrees.pi/5 radians = 36º and

this might be easier to handle if you think in degrees.pi/5 radians = 36º and3pi/10 rad = 54º

this might be easier to handle if you think in degrees.pi/5 radians = 36º and3pi/10 rad = 54ºdid you notice that they add up to 90º and did you know that the cos (any angle) = sin (90 -any angle) ?

this might be easier to handle if you think in degrees.pi/5 radians = 36º and3pi/10 rad = 54ºdid you notice that they add up to 90º and did you know that the cos (any angle) = sin (90 -any angle) ?so cos(36º)= sin(54º) = (1+√5)/4

this might be easier to handle if you think in degrees.pi/5 radians = 36º and3pi/10 rad = 54ºdid you notice that they add up to 90º and did you know that the cos (any angle) = sin (90 -any angle) ?so cos(36º)= sin(54º) = (1+√5)/4BTW, cos 36º is exactly half the Golden Ratio, which would bring me to the Fibonacci numbers and other most fascination topics that I could spend hours ......

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