Question 205196
Remember the Pythagorean theorem {{{c^2 = a^2+b^2}}} that shows the relationship among the three sides of a right triangle, a, b, and c?
C is the hypotenuse (or the diagonal of the computer monitor in this problem) while a and b are the two other sides (horizontal and vertical measurements).
You have measured the diagonal, that's c at 13 inches and you have measured the vertical height, and that's a at 8 inches, so we substitute these (c = 13 and a = 8) into the Pythagorean formula:
{{{c^2 = a^2+b^2}}} 
{{{13^2 = 8^2+b^2}}}
{{{169 = 64+b^2}}} Subtract 64 from both sides of the equation.
{{{105 = b^2}}} Take the square root of both sides.
{{{sqrt(105) = sqrt(b^2)}}} 
{{{highlight(b = 10.25)}}}inches, approximately.