How are expressions rewritten in simplified form based on mathematical operations in the expression

List x1, x2, x3, x4 where xi is the left endpoint of the four equal intervals used to estimate the area under the curve of f(x) between x = 4 and x = 6. a 4, 4.5, 5, 5.5 b 4.5, 5, 5.5, 6 c 4.25, 4.75, 5.25, 5.75 d 4, 4.2, 5.4, 6

If the value of cos330°is√3/2 then find cos 165°.

What is the product? a-3/15a × 5/a-3