Prove that a+(a+b)+(a+2b)+........... {a+(n-1)d} =n÷2×{2a+(n-1)d} by PMI method

Prove that a+(a+b)+(a+2b)+........... {a+(n-1)d} =n÷2×{2a+(n-1)d} by

1.	Prove that a+(a+b)+(a+2b)+........... {a+(n-1)d} =n÷2×{2a+(n-1)d} by PMI method
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