4X²-3X=52
=>
4x^2 - 3x - 52 = 0
4 = 1*4
52 = 4*13
十字相乘
4 13
-3
1 -4
得到(4x + 13)(x-4) = 0
所以x = -13/4 或者x=4
5X²＝4-2X
=>
5x^2 + 2x - 4 = 0
=>
5(x^2 + 2/5 x + 1/25 - 1/25) -4=0
=>
5(x+1/5)^2 = 21/5
=>
(x+1/5)^2 = 21/25
所以
x = (根号(21) - 1)/5
或者
x = (-根号(21)-1)/5十字相乘是什么额 没学过.....你几年级了?十字相乘法没有学过吗?不用十字相乘法的话,4x^2 - 3x - 52 = 0=>4x^2 + 13x - 16x - 52 = 0=>x(4x + 13) - 4(4x +13) = 0=>(4x+13)(x-4) = 0所以x=4 或者x = -13/4