SOLUTION: Solve for R? 100=70/(1+R)+60/(1+R)^2

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Question 104636: Solve for R?
100=70/(1+R)+60/(1+R)^2
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
100=70%2F%281%2BR%29%2B60%2F%281%2BR%29%5E2
10%281%2BR%29%5E2=7%281%2BR%29%2B6 Multiply both side by %281%2BR%29%5E2%2F10.
10%281%2B2R%2BR%5E2%29=7%281%2BR%29%2B6 Expand.
10%2B20R%2B10R%5E2=7%2B7R%2B6 Distribute.
10R%5E2%2B20R%2B10=7R%2B13 Group terms on both sides.
10R%5E2%2B13R-3=0 Group terms on one side.
R=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
where a=10, b=13, c=-3
R=+%28-13%2B-+sqrt%28+13%5E2-4%2A10%2A%28-3%29+%29%29%2F%282%2A10%29+
R=+%28-13%2B-+sqrt%28+169%2B120%29%29%2F%2820%29+
R=+%28-13%2B-+sqrt%28+289%29%29%2F%2820%29+
R=+%28-13%2B-+17%29%2F%2820%29+
First solution
R=+%28-13%2B+17%29%2F%2820%29+
R=1%2F5
Second solution
R=+%28-13-+17%29%2F%2820%29+
R=+-3%2F2+
Let's check one solution
100=70%2F%281%2BR%29%2B60%2F%281%2BR%29%5E2
100=70%2F%286%2F5%29%2B60%2F%2836%2F25%29
100=350%2F6%2B250%2F6
100=600%2F6
100=100
Good answer.
You can also check the other answer.