Question 1042528
The function must be:
{{{ f(x) = 3*sin( ( 2*pi*x )/10 ) }}}
When x = 10, 20, 30, etc
 ( 2*pi*x )/10 = 2pi, 4pi, 6pi, etc.
and these are periods of the sin
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Here's the plot:
{{{ graph( 400, 400, -10, 20, -3, 3, 3*sin( (2*pi*x/10) ) ) }}}
The range is:
{{{ -3 <= f(x) <= 3 }}}
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The x-intercepts are:
-10, -5, 0, 5, 10, 15, 20
The y-intercept is {{{ y = 0 }}}
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The maximums are at:
( -7.5, 3 )
( 2.5, 3 )
( 12.5, 3 )  
The minimums are at:
( -5, -3 )
( 5, -3 )
( 15, -3 )
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The sine function is an odd function which 
means that {{{ f( -x ) = -f(x) }}}