Answers ? For every step

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

How many liters of peroxide should be added to 12 liters of an 8% peroxide solution so that the resulting solution contains 16% peroxide?   original added new amount of peroxide 0.96 liters x 0.96 + x amount of solution 12 liters x 12 + x 0.18 liter 1.14 liters 1.92 liters 2.10 liters

Ratio of circumference to diameter example plz i need to now what it looks like.