Difference of two angles formula: cos (A - B) = cos A cos B + sin A sin B

cos (90 - 50) = cos 90 cos 50 + sin 90 sin 50

cos (90 - 50) = 0 * cos 50 + 1 * sin 50

cos (90 - 50) = 0 + sin 50





OR



Shortcut

sin and cos are COFUNCTIONS, so cos (90 - 50) = cos 40 = sin (90 - 40), or sin 50 

RELATED QUESTIONS

Please show work and use a product of sines and cosines formula to rewrite cos(5t)... (answered by lwsshak3)

Use one of the product-to-sum formulas to write the given 
product as a sum of sines or... (answered by Edwin McCravy)

Use one of the formulas product-to-sum to write the given product as a sum of sines or a... (answered by robertb)

Use Theorems about sines and cosines to prove that sin(pi-theta) =... (answered by stanbon)

verify the identity. convert to sines and cosines.

cscθ - sinθ =... (answered by josgarithmetic)

Hi!
if I have the following information for a triangle:
a=16, b=20 angle B=40

is it... (answered by edjones)

 Write each expression in terms of sines and/or cosines and then simplify.... (answered by MathLover1,mananth,Edwin McCravy)

Rewrite the product as a sum involving sine and/or cosine... (answered by stanbon)

(1). Simplify the trigonometric expression to a multiple or power of a single trig... (answered by lwsshak3)