divide [a] square+6a+5 bya+1

^{2} + 6a + 5 by splitting the middle term

a^{2} + 6a + 5

= a^{2} + 5a + a + 5 (note that 6 = 5 + 1 and 5 = 5×1)

= a(a + 5) + 1(a + 5)

= (a + 5)(a + 1)

Hence we can see that a + 1 is a factor of a^{2} + 6a + 5

OR

When a^{2} + 6a + 5 is divided by a + 1, the quotient left is 'a +5' and remainder is 0.

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