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# For each positive integer n, the quantity sn is defined such that sn

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Re: For each positive integer n, the quantity sn is defined such that sn [#permalink]
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Given: sn+2=(sn)2−sn+1
S2 = 1.

When we substitute values for S3 and S4 we get:
S3 = S1^2 - S2.
S4 = S2^1 - S3 => S4 = S2^1 - S1^2 + S2,
Now Substituting S2 =1, we get:
S4 + S1^2 = 2.

Only 2 values satisfy the given condition: S4 = -7, S1 = -3
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Re: For each positive integer n, the quantity sn is defined such that sn [#permalink]
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Here,

S3= S1^2-S2
S4=S2^2-S3
S4= S2^2-S1^2+S2
Now S2=1
S4=2-S1^2
So checking from options

S4=-7,S1=-3

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Re: For each positive integer n, the quantity sn is defined such that sn [#permalink]
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S4= s2^2-S3
S3=s1^2-1

S4 = s2^2-s1^2+1
S4= 2-s1^2

Values are given in negative it means s4 could be negative it means s1 mode should be higher than 2
Try s1= -3
S2 comes out to be -7
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Re: For each positive integer n, the quantity sn is defined such that sn [#permalink]
KarishmaB GMATinsight chetan2u WOuld you like to explain this question ?­
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For each positive integer n, the quantity sn is defined such that sn [#permalink]
parkhydel wrote:
For each positive integer n, the quantity $$s_{n}$$ is defined such that $$s_{n + 2} = (s_{n})^2 − s_{n + 1}$$. In addition, $$s_{2} = 1$$.

Select values for $$s_{1}$$ and $$s_{4}$$ that are jointly compatible with these conditions. Make only two selections, one in each column.­

ID: 100402

­
$$s_{n + 2} = (s_{n})^2 − s_{n + 1}$$

$$s_3 = (s_1)^2 − s_2 = (s_1)^2 − 1$$

$$s_4 = (s_2)^2 − s_3 = 1^2 - ((s_1)^2 − 1) = 2 - (s_1)^2$$

Hence s1 and s4 satisfy this condition:
$$s_4 = 2 - (s_1)^2$$

If s1 is -3, s4 = -7