It's a modulus of the function; so everything in the negative y flips over to positive y. Imagine 40 of those 'humps' (with area A) going across and you can find out where the last one hits the x-axis, that would be your kπ
Sub kpi and zero into integral and equate it to 40*your A?
No need to mess around with any integrals, to be honest, that would just take longer. Observe the pattern of the modulus. If the boundary for A is between 0 and 4π, then obviously the boundary for 40A would be between 0 and 40⋅4π
It's a modulus of the function; so everything in the negative y flips over to positive y. Imagine 40 of those 'humps' (with area A) going across and you can find out where the last one hits the x-axis, that would be your kπ
I didn't notice that. Thanks for the help, its a whole lot clearer now.