charlie_eppes wrote:[tex]|{a_{5}}^{2}-{a_{3}}^{2}=72[/tex]
[tex]|a_{5}+a_{8}=28[/tex]
Something is wrong in my answers. I can't define it.
And this
[tex]|5a_{1}+10a_{5}=0[/tex]
[tex]|S_{4}=14[/tex]
a5^2 – a3^2 = 72, a5 + a8 = 28, find a1 and d
(a1 + 4d) + (a1 + 7d) = 2a1 + 11d = 28 or a1 = (28 – 11d)/2
(a1 + 4d)^2 – (a1 + 2d)^2 = a1^2 + 16d^2 + 8a1d – a1^2 – 4d^2 – 4a1d = 12d^2 + 4a1d = a2d^2 + 4d(28 – 11d)/2 = 12d^2 + 56d – 22d^2 = 72
Or -10d^2 + 56d = 72 or 5d^2 – 28d + 36 = (5d – 18 )(d – 2) = 0 or d = 2
a1 = (28 – 11d)/2 = 14 – 11 = 3