Question 701596
 determine the first three terms of the arithmetic progression of which : 
the 4th term is -13 and the 7th term is -25 
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Equations:
a + 3d = -13
a + 6d = -25
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Subtract and solve for "d":
3d  -12
d = -4
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Solve for "a":
a + 3d = -13
a + 3*-4 = -13
a = -1
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1st 4 terms: -1, -1+-4 = -5 ; -5+-4 = -9
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Cheers,
Stan H.
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