You can not divide by zero in math.
The surface of the rectangular prism is 18, because you just add up all of your sides
<span>Larger angle measures four degrees more than seven times the smaller angle. ... The measure of one of two complementary angles is 21 less than twice the measure of the other angle. ... One angle is 4 degree less than 3 times the other.</span><span>
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From my understanding you ahould use the trig function cos to solve this.
cos(c) = 15/25 or 0.6
if you have this following function on your calculator I suggest using it:
cos ^{ - 1}
by using the function like so:
cos^{ - 1} (0.6
you should get about 53.13° (rounding to the nearest hundredth)
Hope this helped.
