若等差数列An满足a2+s3=4,a3+s5=12,则a4+s7为多少
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![若等差数列An满足a2+s3=4,a3+s5=12,则a4+s7为多少](/uploads/image/z/2427911-71-1.jpg?t=%E8%8B%A5%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97An%E6%BB%A1%E8%B6%B3a2%2Bs3%3D4%2Ca3%2Bs5%3D12%2C%E5%88%99a4%2Bs7%E4%B8%BA%E5%A4%9A%E5%B0%91)
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若等差数列An满足a2+s3=4,a3+s5=12,则a4+s7为多少
若等差数列An满足a2+s3=4,a3+s5=12,则a4+s7为多少
若等差数列An满足a2+s3=4,a3+s5=12,则a4+s7为多少
a2+a1+a2+a3=4 ,a2=1.a3+a1+a2+a3+a4+a5=12,a3=12.所以a4+s7=24
24
s3=3(a2) => a2=1
s5=5(a3) => a3=2
=> a4=3
s7=7(a4)
所以a4+s7=8(a4)=24
a2+s3=4
a2+3a2=4
a2=1
a3+s5=12
a3+5a3=12
a3=2
a4=2a3-a2=2*2-1=3
a4+s7=a4+7a4=8a4=8*3=24