已知y1=a2+b2,y2=y1-3,且y1•y2=4,则y1的值为( )A.4B.-1C.-4或1D.-1或4
题型:单选题难度:一般来源:不详
已知y1=a2+b2,y2=y1-3,且y1•y2=4,则y1的值为( ) |
答案
∵y1=a2+b2,y2=y1-3, ∴y2=a2+b2-3, ∵y1•y2=4, ∴(a2+b2)(a2+b2-3)=4, 解得a2+b2=-1或4, ∵a2+b2≥0, ∴a2+b2=4. 故选A. |
举一反三
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