Question

这道数学题怎么做求解答谢谢！

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Answer 1

(2x^2+8x+20)-(x^2+4x+5)
=2x^2+8x+20-x^2-4x-5
=x^2+4x+15
=(x+2)^2-4+15
=(x+2)^2+11>游轮0
所神凳信粗陆以 2x^2+8x+20 > x^2+4x+5

Answer 2

(28)

2x^2+8x+20 -(x^2+4x+5)
=x^2+4x+15
=(x+2)^2 +11
>0
=>数迅粗薯镇昌漏
2x^2+8x+20 >x^2+4x+5
(2)
(1) 1∈Z
(2) 1∈{x|x^2=1}
(3) Φ⊊ {1}

Answer 3

比较大小，可以用减法：
2x²+8x+20-（x²+4x+5）闹简衫=2x²+8x+20-x²-4x-5
=x²+4x+15
=x²+4x+4+11
=（x+2）²+11＞咐携0
所以，2x²+8x+20＞液腔x²+4x+5