What’s 90% as a fraction in simplest form

Find the magnitude, correct to two decimal places, made by each of the following with positive direction of the x axis a) y= x the answer is 45° but i don’t know how

Graph the equationy=x^2 -[tex]y = x^{2} - 2[/tex]

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab