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a=16x^2+7y^2 and b=15xy

(16x^2+7y^2+15xy) (16x^2+7y&2−15xy)

Step-by-step explanation:

If we draw a right triangle with an angle of 19° in it, then the other angle is  90° - 19° = 71° (because all angles in a triangle add up to 180°).see attached diagram. let y be the opposite side to 19°, let x be its adjacent, let r be hypotenuse.cosine is adjacent/hypotenuse, so  for 71° to get the same ratio, we use the sine of that angle.since these are the same thing, the answer is a