Question

why cos^-1(cos7pi/6)=5pi/6

Answer 1

it should be 7pie/6

Answer 2

its given 5pi/6 in the textbook

Answer 3

well,cos(2pi-theta)= cos(theta) isn't it?

Answer 4

cos^-1 (cos 2pie - 5pie/6) = 5pie/6

Answer 5

careful with brackets @Yahoo!

Answer 6

because \(\cos^{-1}(x)\) does not mean "any number whose cosine is \(x\)" but rather it means
" the number between 0 and \(\pi\) whose cosine is \(x\)"

Answer 7

since \(\frac{7\pi}{6}\) is evidently larger than \(\pi\) , it is not in the range of \(\cos^{-1}(x)\)
you need another number in the interval \([0,\pi]\) with the same cosine

Answer 8

@drown ,u still have doubts??