a2+a4=42
a3+a5=126
a1q+a1q^3=42
a1q^2+a1q^4=126
a1q(1+a1q^2)=42
a1q^2(1+a1q^2)=126
q=126/42
q=3
3a1+27a1=42
30a1=42
a1=42/30
an=42/30*3^(n-1)
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a2+a4=42
a3+a5=126
a1q+a1q^3=42
a1q^2+a1q^4=126
a1q(1+a1q^2)=42
a1q^2(1+a1q^2)=126
q=126/42
q=3
3a1+27a1=42
30a1=42
a1=42/30
an=42/30*3^(n-1)