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##### Two wires support a utility pole and form angles alpha and beta...

label Calculus
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schedule 0 Hours
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…with the ground. Find the value of tan(alpha + beta) if sin alpha = 3/5 on the interval (0degrees, 90degrees) and tan beta = radical 15 on the interval (0degrees, 90 degrees).

Oct 18th, 2017

Okay, first, you have to know that the tan(A + B) = (tanA + tanB)/(1-tanAtanB). You can learn to derive this formula - or just memorize it.

Next, given an angle with a sin = 3/5, the tangent must equal 3/4. To see why, draw a right triangle and label one of the acute angles A. Since sinA=3/5 the opposite side must be 3 and the hypotenuse must be 5. The only value possible for the adjacent side is 4 since it must be a 3,4,5 right triangle (pythagorean theorem). So the tangent is opp/adj. or 3/4.

(The bit about the angle being between 0 and 90 is important because without it the sin could be 3/5 but the tangent could be negative 3/4 - if the angle was in the second quadrant.)

Jan 29th, 2015

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Oct 18th, 2017
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