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Polynomial

The polynomial p(x) is defined by p(x) = 2 x^3 + ax^2 -21x + b, where a and b are constants. P(x) has a factor of (x + 3) and a remainder of 20 when it is divided by (x-2)

Determine the values of a and b:

Is this correct??

F(2): 20= 2(2)^3 + a (2)^2 - 21(2) + b

46= 4a + b

f(-3)=2(-3)^3 + a(-3)^2 - 21(-3) + b

=9a+b+9

So a=11 and b =2

b) solve p(x)=0, for this I've subbed in the a and b values and used factor (x+3)