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Ask for a detailed explanation of the math 13 of the 2008 college entrance examination in Jiangsu Province.
Suppose the angle BAC=X, because the length of BA AC is known. This triangle is definite. Then calculate the area.

High CD with c as AB surface. Just draw a picture yourself.

If x & gt90, CD = AC * sin (x-90).

If x < 90, CD=AC*sinx.

Therefore, if and only if x = 90, CD is always less than or equal to AC.

Therefore, when the maximum area of triangle ABC is angle BAC = 90. Area root number 2