等差数列a1+a6=9,a4=7,求a3,a9

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等差数列a1+a6=9,a4=7,求a3,a9等差数列a1+a6=9,a4=7,求a3,a9等差数列a1+a6=9,a4=7,求a3,a9等差数列a1+a6=9,a4=7,求a3,a92a1+5d=9

等差数列a1+a6=9,a4=7,求a3,a9
等差数列a1+a6=9,a4=7,求a3,a9

等差数列a1+a6=9,a4=7,求a3,a9
等差数列a1+a6=9,a4=7,求a3,a9
2a1+5d=9(1)
a1+2d=7(2)
(1)-(2)×2得:
d=9-14=-5;
带入(2)得:
a1-10=7;
a1=17;
∴a3=a1+2d=17-10=7;
a9=a1+8d=17-40=-23;
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