Question

Simplify 7x2(3x – 9) + 3 and find its values for x = 4 and x = 6

Answer 1

Answer:

7x2(3x – 9) + 3

Solve for 7x2(3x – 9)

= (7x2 × 3x) – (7x2 × 9) (using distributive law: a(b – c) = ab – ac)

= 21x3 – 63x2

So, 7x2(3x – 9) + 3

= 21x3 – 63x2 + 3

Now, for x = 4,

21x3 – 63x2 + 3

= 21 × 43 – 63 × 42 + 3

= 1344 – 1008 + 3

= 336 + 3 = 339

Now, for x = 6,

21x3 – 63x2

= 21 × 63 – 63 × 62 + 3

= 2268 + 3

= 2271