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x乘以2x等于2x²吗,为什么

Sn=x+2x²+3x³+...+nx^n ① x×Sn=x²+2x³+3x^4+...+nx^(n+1) ② ①-②得 Sn-xSn=x+x²+x³+...+x^n-nx^(n+1) =【x-x^(n+1)】/(1-x)-nx^(n+1) (1-x)Sn=【x-x^(n+1)】/(1-x)-nx^(n+1) Sn=【x-x^(n+1)】...

∫(0→2) x√(2x - x²) dx = ∫(0→2) x√[1 - (x - 1)²] dx 令x - 1 = sinθ,dx = cosθdθ,第二换元积分法 当x = 0,θ = - π/2 当x = 2,θ = π/2 = ∫(- π/2→π/2) (1 + sinθ) * cos²θ dθ = ∫(- π/2→π/2) cos²θ dθ + ∫(- π/2→π/2) sinθ...

解: f(x)=x²(x-2)²-a(x-1) f'(x) =[x²(x-2)²-a(x-1)]' =2x(x-2)²+x²(2x-4)-a =2x(x-2)²+2x²(x-2)-a =2x(x-2)(x-2+x)-a =4x(x-2)(x-1)-a

(2x的余弦值乘以x的余弦值)加上(3x的正弦值乘以x的正弦值) =(cos2xcosx)+(sin3xsinx) =(2cos²x-1)cosx+(3sinx-4sin³x)sinx =(2cos³x-cosx)+(3-4sin²x)sin²x =(2cos³x-cosx)+[3-4(1-cos²x)](1-cos²x) =(...

20×40+(20+2x)×(40-x)=1200 800+800-20x+80x-2x²=1200 2x²-60x-400=0 x²-30x-200=0 (x-15)²-425=0 (x-15)²=425 x-15=±5√17 x=15±5√17

(x-3)²=4(2x+1)² [(4x+2)]²-(x-3)²=0 (4x+2+x-3)(4x+2-x+3) = 0 (5x-1)(3x+5) = 0 x1 = 1/5 x2 = -5/3

5×(3x)²-5×(2x)²=1, 5×5x²=1, x²=1/25, x=1/5,或x=-1/5

解: 2乘以x² =2x² 这个就是最简表达式 具体等于多少,要看x=多少 例如x=2 2x²=8 x=3 2x²=28 等等

三分之一x的平方减去2x减去3327等于0 两边同乘以3得: x²-6x-9981=0 x²-6x=9981 x²-6x+9=9981+9 (x-3)²=9990 x-3=±3√1110 x=3±3√1110

x(x+4)=6x+12 x²+4x=6x+12 x²-2x=12 x²-2x+1=12+1 (x-1)²=13 x-1=±√13 x=1±√13 x₁=1+√13、x₂=1-√13

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