展开 (7e+9f)(7e-9f)

解答

展开

(7 e + 9 f) (7 e - 9 f)

- 81 f^{2} + 49 e^{2}

求解步骤

(7 e + 9 f) (7 e - 9 f)

使用平方差公式:

(a + b) (a - b) = a^{2} - b^{2}

a = 7 e, b = 9 f

= (7 e)^{2} - (9 f)^{2}

化简

(7 e)^{2} - (9 f)^{2} : - 81 f^{2} + 49 e^{2}

= - 81 f^{2} + 49 e^{2}

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