You can put this solution on YOUR website! So the rectangle is 12 long by 7 wide.
The diagonal cuts the rectangle into two right triangles
The length of the diagonal = sqrt(12^2 + 7^2) = 13.9
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So we have a right triangle with long side 12 and short side 7, with a hypotenuse 13.9
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You've probably heard of SOHCAHTOA. In this case, we'll use SOH
Sine: sin(θ) = Opposite / Hypotenuse
= sin(x) = Opposite / Hypotenuse = 7 / 13.9 = 0.5036
Let's rearrange it like this:
x = sin^-1(0.5036) = 30.24 degrees
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Here's a drawing for you:
