How to solve it by wavy curve method?? I am confused how to take values of x( i.e.x belongs to) if the condition is less than or equal and greater than or equal to 0 .

first off draw the wavy curve. then for all those intervals where the wave is ABOVE the number line, the function is greater than 0. and for all those intervals where the wave is BELOW the number line, the function is less than 0. if you still have any doubts, you must visit the page on brilliant dot org as it explains this concept with crystal clarity :) kindly approve