Given x > = 3, compare the size relation of X & # 178; - 1 and 2x + 2 | Math enthusiast | Mathematical art

Given x > = 3, compare the size relation of X & # 178; - 1 and 2x + 2

(x²-1)-(2x+2)
=(x+1)(x-1)-2(x+1)
=(x+1)(x-3)
x>=3
Then x + 1 > 0
x-3>=0
So (X & # 178; - 1) - (2x + 2) > = 0
x²-1>=2x+2

If x + y = 52X + y = 8, then x + 2Y=______ ．

(1) (2) we get: - x = - 3, x = 3. Substituting x = 3 into (1) we get: 1 + y = 5, y = 2. X + 2Y = 3 + 2 × 2 = 7

If x > y, compare the formula 2x + y with x + 2Y

2x+y-x-2y
=x-y>0
therefore
2x+y>x+2y

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