標題:
mathsssssss!!
發問:
a2 - b2 = -16 ab=15 求a, b 更新: 我要埋條式 唔該晒
最佳解答:
a2 - b2 = -16.........(1) ab=15.......(2) From (2) a = 15/b.........(3) Substitute (3) into (1) (15/b)2 – b2 = -16 225/b2 – b2 = -16 225 – b4 = -16b2 b4 – 16b2 – 225 = 0 (b2 – 25)(b2 + 9) = 0 b2 = 25 or b2 = -9 (rejected because b2 must >= 0) b = 5 or -5 when b=5, a = 15/5 = 3 when b=-5, a = 15/-5 = -3 Therefore a=3 and b=5 Or a=-3 and b=-5
a=3, b=5a=15/b a2=225/b2 225/b2-b2=-16 16=(b2-225)b2 16b2=b2-225 15b2=-225 b2=-15 no solutiona=3 b=5
mathsssssss!!
發問:
a2 - b2 = -16 ab=15 求a, b 更新: 我要埋條式 唔該晒
最佳解答:
a2 - b2 = -16.........(1) ab=15.......(2) From (2) a = 15/b.........(3) Substitute (3) into (1) (15/b)2 – b2 = -16 225/b2 – b2 = -16 225 – b4 = -16b2 b4 – 16b2 – 225 = 0 (b2 – 25)(b2 + 9) = 0 b2 = 25 or b2 = -9 (rejected because b2 must >= 0) b = 5 or -5 when b=5, a = 15/5 = 3 when b=-5, a = 15/-5 = -3 Therefore a=3 and b=5 Or a=-3 and b=-5
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其他解答:a=3, b=5a=15/b a2=225/b2 225/b2-b2=-16 16=(b2-225)b2 16b2=b2-225 15b2=-225 b2=-15 no solutiona=3 b=5
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