Le point M se déplace sur le segment [BC].
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triangles rectangles
ABM et DCM aient la
même aire ? Justifier.​

x must be 13

Step-by-step explanation:

Represent the nine scores by a, b, c, d, e, f, g, h, i.

Write the following equation to indicate that the average of these nine scores is 8:

a+b+c+d+e+f+g+h+i

= 8, or a+b+c+d+e+f+g+h+i = 72 if we multiply both

               9                      sides of this equation by 9.

Next, we add scores x and x+ 1 to

a+b+c+d+e+f+g+h+i  +  x + x + 1

and divide the result by 11, as there are now 11 scores instead of just 9:

a+b+c+d+e+f+g+h+i  +  x + x + 1

                        11

Earlier, we saw that a+b+c+d+e+f+g+h+i = 72.  We can now replace

a+b+c+d+e+f+g+h+i in the above fraction by 72:

 72 + 2x + 1

= 9 (as the new average is 9)

         11

Multiplying both sides of this equation by 11 results in:

73 + 2x = 99, or  2x = 26.

Then x must be 13, and x + 1 must be 14.