177 25 Marks Rajesh is working out the area of a circle with radius 10.
He writes:
Area = 3.142 x 20
Explain why Rajesh's working is wrong.

Rajesh did πr2 (π × r × 2) instead of πr². The correct work would be

Area = 3.142 x 10²  so... Area = 3.142 x 100 not 3.142 x 20.

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb