Count them all!

Geometry Level 4

Find number of real solutions of x = 99 sin ( π x ) . x = 99\sin(\pi x).


The answer is 199.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Tom Engelsman
Feb 12, 2017

Clearly ( x , y ) = ( 0 , 0 ) (x,y) = (0, 0) is one solution. The range of the sine curve is contained in [ 99 , 99 ] [-99, 99] , which occur at the abscissae:

x = 0.5 , 2.5 , 4.5 , . . . , 98.5 x = {0.5, 2.5, 4.5, ... , 98.5} for maximum of 99.

x = 0.5 , 2.5 , 4.5 , . . . , 98.5 x = {-0.5, -2.5, -4.5, ... , -98.5} for minimum of -99

Each of these sine peaks contains two points of intersection with the line y = x y = x . The curves will no longer intersect each other in ( , 99 ] [ 99 , + ) (-\infty, -99] \cup [99, +\infty) . So we ultimately end up with: 50 2 50 \cdot 2 RHS points + 50 2 50 \cdot 2 LHS points - 1 point (the repeated origin ( 0 , 0 ) (0,0) ) = 199 \boxed{199} total intersection points.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...