x(x-1)/2=45

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x(x-1)/2=45x(x-1)/2=45x(x-1)/2=45x(x-1)/2=45x(x-1)=45×2x²-x=90x²-x-90=0(x-10)(x+9)=0x-10=0

x(x-1)/2=45
x(x-1)/2=45

x(x-1)/2=45
x(x - 1)/ 2 = 45
x(x - 1)= 45 × 2
x ² - x = 90
x ² - x - 90 = 0
(x - 10)(x + 9)= 0
x - 10 = 0 x + 9 = 0
x1 = 10 x2 = - 9


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x^2-x-90=0
(x-10)(x+9)=0
x=-9或10

x(x-1)/2=45
x²-x=90
x²-x-90=0
(x-10)(x+9)=0
x1=10, x2=-9

x(x-1)/2=45
x(x-1)=90
x^2-x-90=0
(x-10)(x+9)=0
x1=10 x2=-9

题目:x(x-1)/2=45
x^2-x=90
化简得: x^2-x-90=0
合并:(x-10)(x+9)=0
∴x=10或x=-9

=> x^2 -x =90 => x^2 -x -90=0=(x-10)(x+9) => x=10; -9

x^2-x-90=0
(x-10)(x+9)=0
x=10或者x=-9