Question 1027996
For any angle {{{x}}} of a right triangle, let {{{a}}} be the adjacent side of the angle and {{{b}}} be the opposite side of the angle and {{{c}}} be the hypotenuse of the triangle.
From the Pythagorean theorem,
{{{a^2+b^2=c^2}}}
But you also know from trigonometry,
{{{cos(x)=a/c}}}
{{{sin(x)=b/c}}}
So then continuing from the equation above,
{{{a^2/c^2+b^2/c^2=1}}}
{{{cos^2(x)+sin^2(x)=1}}}