Let the degree of this angle be x, then its complementary angle is 90-X,

X=2*(90-X)，X=60

So its complementary angle = 180-60= 120 degrees.

2.

y^2+y+ 1/4=(y+ 1/2)^2

3.

When the side length increases, it is a+5, and the area is (A+5) 2.

So the increased area:

(a+5)^2-a^2

=(a+5+a)(a+5-a)

=(2a+5)*5

= 10a+25

4.

S= bottom * height /2

Height16a4-2a2+1/4 = (4a-1/2) 2

So s = 1/2 * (4a+ 1/2) 3.

5.

75/ 100=7.5* 10^(- 1)