Question 1130815
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Although not clearly stated in the problem, theta is the angle between the two sides of length 7.<br>
If you need to use the formula {{{A = (1/2)(7^2)sin(theta)}}} to solve the problem, then consider one of the legs of length 7 as the base; then the height of the triangle is the length of the other leg of length 7, multiplied by sin(theta).  So clearly the area is maximum when sin(theta) is maximum -- which is at 90 degrees.<br>
You don't really need the formal mathematical formula to find that result.  With one of the legs of length 7 the base, the height of the triangle is the distance from the end of the other leg of length 7 to the base; obviously that distance is the greatest when the angle is 90 degrees.