Answer
$8 \cos^{2}\theta +2\cos\theta -15$
Work Step by Step
Given expression is-
$ (2\cos\theta+3) (4\cos\theta-5)$
= $ 2\cos\theta . 4\cos\theta +2\cos\theta .(-5) +(3) 4\cos\theta -15$
= $ 8\cos^{2}\theta -10\cos\theta +12\cos\theta -15$
( By FOIL method)
= $8 \cos^{2}\theta +2\cos\theta -15$
