數學問題!!!有兩題?

2019-07-25 7:57 pm
(1) a-b=7,ab=-5,求a+b=?
(2) 2094*1906=2000^2-a^2,則a=?(此題有兩個答案)

回答 (2)

2019-07-25 8:00 pm
✔ 最佳答案
1 a-b=7,ab=-5,求a+b=?
Sol
(a+b)^2
=(a-b)^2+4ab
=7^2+4*(-5)
=29
a+b=+/-√29
2. 2094*1906=2000^2-a^2,則a=?
Sol
a^2=2000^2-2094*1906
=2000^2-(2000+4)*(2000-4)
=2000^2-(2000^2-16)
=16
a=+/-4
2019-07-25 9:45 pm


a + b = ±√[(a - b)² + 4ab]

= ±√[7² + 4(-5)]

= ±√29



2094 × 1906

= (2000 + 94)(2000 - 94)

= 2000² - 94² = 2000² - a²


a² = 94²

a = ±94 #


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