What is the value of x?

What basic trigonometric identity would you use to verify that sin x cos x tan x =1-cos^(2)x?

Iam trying to solve a linear equation for the shoe size of someone 84" tall taking into consideration example 1 is 69" tall with a shoe size of 9 and example 2 is 72 inches tall with a shoe size of 11. i understand that the equation should be y=mx+b and that on the graph the answer is (3,2) but i just don't understand how to create the equation to solve for 84-inches and 60-inches tall questions. after two days, i need .

Write a function for a rotation 90 degrees counter clockwise about the origin, point 0