F4 quadratic equations

2009-09-25 8:47 pm

One number is four times the other number. If each number is increased by 5, the
product of the two new numbers is 91. Find the two original numbers.

回答 (1)

2009-09-25 9:20 pm

✔ 最佳答案

Let the numbers are x and 4x. Then
(x+5)(4x+5)=91
4x^2+25x+25-91=0
4x^2+25x-66=0
(4x+33)(x-2)=0
x=-33/4 or x=2
So, the two numbers are 2 and 8

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