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anonymous

  • 5 years ago

y=2x is a tangent to the curve y=x^3+ax+b at x=1. Find a and b.

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  1. bahrom7893
    • 5 years ago
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    Tangent line is the first derivative, so: y' = 3x^2 + a; x = 1; y' = 3*1^2 + a

  2. bahrom7893
    • 5 years ago
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    3 + a = y'

  3. bahrom7893
    • 5 years ago
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    now slope of ur tangent line is: y= 2x; M = 2=> 3 + a = 2 => a = -1

  4. bahrom7893
    • 5 years ago
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    but what the heck is b? lol im lost lemme see, kinda embarassing

  5. anonymous
    • 5 years ago
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    wouldn't i just fill in a & fill in 1 for x to find b?

  6. bahrom7893
    • 5 years ago
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    oh yeah, i think you do this: you need y too when x=1, so y = 2x = 2; x = 1; a = -1 2 = 1^3 + (-1)*1 + b 2 = 1 -1 +b => b = 2

  7. bahrom7893
    • 5 years ago
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    can u check the answer?

  8. anonymous
    • 5 years ago
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    yes that's right thank you so much!

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