# How do you express #cos( (3 pi)/ 2 ) * cos (( 5 pi) /4 ) # without using products of trigonometric functions?

##### 2 Answers

Feb 26, 2016

0

#### Explanation:

From knowledge of the graph of cosx , we know that

#cos((3pi)/2) = 0# and

#cos((5pi)/4) = -cos(pi/4) = -1/sqrt2 #

#rArr cos((3pi)/2) . cos((5pi)/4) = 0.(-1/sqrt2) = 0 #

Feb 26, 2016

It is equivalent to

#### Explanation:

To express

Although,