题目内容
3.解方程组:$\left\{\begin{array}{l}{{a}_{1}-{a}_{1}{q}^{4}=90}\\{{a}_{1}q-{a}_{1}{q}^{3}=36}\end{array}\right.$.分析 $\left\{\begin{array}{l}{{a}_{1}-{a}_{1}{q}^{4}=90}&{①}\\{{a}_{1}q-{a}_{1}{q}^{3}=36}&{②}\end{array}\right.$,②÷①可得:$\frac{q}{1+{q}^{2}}$=$\frac{2}{5}$,解得q,进而解出a1.
解答 解:$\left\{\begin{array}{l}{{a}_{1}-{a}_{1}{q}^{4}=90}&{①}\\{{a}_{1}q-{a}_{1}{q}^{3}=36}&{②}\end{array}\right.$,
②÷①可得:$\frac{q}{1+{q}^{2}}$=$\frac{2}{5}$,解得q=2或$\frac{1}{2}$.
∴$\left\{\begin{array}{l}{{a}_{1}=-6}\\{q=2}\end{array}\right.$,或$\left\{\begin{array}{l}{{a}_{1}=96}\\{q=\frac{1}{2}}\end{array}\right.$.
∴方程组的解为:$\left\{\begin{array}{l}{{a}_{1}=-6}\\{q=2}\end{array}\right.$,或$\left\{\begin{array}{l}{{a}_{1}=96}\\{q=\frac{1}{2}}\end{array}\right.$.
点评 本题考查了指数幂的运算性质、方程组的解法,考查了计算能力,属于中档题.
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