Thanks very much Alan, 
*** points P and R in the first picture ( x - t ) is a turning point but how did you know that p is the maimum velocity and R is minimum ? ***
I have assumed that P and R are points of inflection.
If this is the case then at P on the x-t graph has the steepest positive gradient hence it will have maximum velocity.
And
R on the x-t graph has the steepest negative gradient hence it will have the greatest negative velocity.
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Remember 3*15,
The gradient on the x-t curve IS dy/dx which IS the velocity.
and
The gradient on the v-t curve is dv/dx which IS the acceleration.
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