Question

if cos(a-b)+1=0 then prove that cosa + cosb =0
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Answer 1

Step-by-step explanation:

if you simplify this

cos(a-b) = -1

a-b= (2n+1)π

a=b+(2n+1)π

cosa = cos(b+(2n+1)π)

which can be written as -cosb

if you don't understand than put n=0

then

you will get cos(π+b) = -cosb