Calculate  f(-7) if f(7)=7 f(x)= ax^7 + bx^3 + cx - 7

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f(x) = ax^7 + bx^3 + cx -7

f(7) = a(7)^7 + b(7)^3 + c(7) -7 = 7

   ==> (7^7)a + (7^3)b + 7c = 14.........(1)

f(-7) = a(-7)^7  + b (-7)^3 + c(-7)-7

         = -1(a(7^7) - b (7^3) - c(7) - 7

          = -[ a(7^7) + b(7^3) +...

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f(x) = ax^7 + bx^3 + cx -7

f(7) = a(7)^7 + b(7)^3 + c(7) -7 = 7

   ==> (7^7)a + (7^3)b + 7c = 14.........(1)

f(-7) = a(-7)^7  + b (-7)^3 + c(-7)-7

         = -1(a(7^7) - b (7^3) - c(7) - 7

          = -[ a(7^7) + b(7^3) + 7c)] -7

But from (1) we know that inside brackets equals 14

         = =>  -(14) -7 = -21

==> f(-7) = -21

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