已知x^2-5x=4,求2x^3-10x^-8x+7的值

来源:学生作业学帮网 编辑:学帮网 时间:2024/05/31 11:18:13

已知x^2-5x=4,求2x^3-10x^-8x+7的值

答:
因为:x²-5x=4
所以:x²=5x+4
所以:
2x³-10x²-8x+7
=2x(5x+4)-10x²-8x+7
=10x²+8x-10x²-8x+7
=7

已知x^2-5x=4
所以x^2=5x+4
所以2x^3-10x^2-8x+7
=2x*x^2-10x^2-8x+7
=2x(5x+4)-10x^2-8x+7
=10x^2+8x-10x^2-8x+7
=7
如果不懂,请追问,祝学习愉快!