In the quadrilateral ABCD, AC = x + 6
and
BD = 2x– 4
For what value of x is ABCD a rectangle?

What is the value of x when x + 7 = 21?

If tan2a=cot(a+60), find the value of a, where 2a is an acute angle

Given the system of equations presented here: 2x + 4y = 14 4x + y = 20 which of the following actions creates an equivalent system such that, when combined with the other equation, one of the variables is eliminated? multiply the second equation by â’4 to get â’16x â’ 4y = â’80 multiply the second equation by â’1 to get â’4x â’ y = â’20 multiply the first equation by 2 to get 4x + 8y = 28 multiply the first equation by â’1 to get â’2x â’ 4y = â’14