The polynomial p(x) is defined by p(x) = 4x³ + 4x² – 29x – 15.
- (i)Use the factor theorem to show that (x + 3) is a factor of p(x).[2]
- (ii)Factorise p(x) completely.[3]
- (iii)Hence, given that 2³u+2 + 4u+1 = 29 × 2u + 15, find the value of 2u and, using logarithms, find the value of u correct to 3 significant figures.[3]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.
- [M1] Substitute x = -3 and simplify
- [A1] Obtain -108+36+87-15=0 or equivalent and conclude
- [M1] Attempt either division by x + 3 to reach at least partial quotient 4x² + kx or use of identity or inspection
- [A1] Obtain quotient 4x² - 8x - 5
- [A1] Conclude (x + 3)(2x - 5)(2x + 1)
- [B1] Identify 2u = 5/2 (Ignoring other values at this stage)
- [M1] Apply logarithms and use power law for 2u = c where c > 0
- [A1] Obtain u = 1.32 And no other values
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →