已知实数x ,y 满足x^2+3x+y-3=0,则x+y的最大值为?解题步骤中的问题解题步骤:令x+y=k解得y=k-x代入x^2+3x+y-3=0得x^2+3x+k-x-3=0x^2+2x+k-3=0令△=4-4(k-3)=0解得k=4故x+y的最大值为4这里为何令△=4-4(k-3)=0?
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![已知实数x ,y 满足x^2+3x+y-3=0,则x+y的最大值为?解题步骤中的问题解题步骤:令x+y=k解得y=k-x代入x^2+3x+y-3=0得x^2+3x+k-x-3=0x^2+2x+k-3=0令△=4-4(k-3)=0解得k=4故x+y的最大值为4这里为何令△=4-4(k-3)=0?](/uploads/image/z/7084182-30-2.jpg?t=%E5%B7%B2%E7%9F%A5%E5%AE%9E%E6%95%B0x+%2Cy+%E6%BB%A1%E8%B6%B3x%5E2%2B3x%2By-3%3D0%2C%E5%88%99x%2By%E7%9A%84%E6%9C%80%E5%A4%A7%E5%80%BC%E4%B8%BA%3F%E8%A7%A3%E9%A2%98%E6%AD%A5%E9%AA%A4%E4%B8%AD%E7%9A%84%E9%97%AE%E9%A2%98%E8%A7%A3%E9%A2%98%E6%AD%A5%E9%AA%A4%EF%BC%9A%E4%BB%A4x%2By%3Dk%E8%A7%A3%E5%BE%97y%3Dk-x%E4%BB%A3%E5%85%A5x%5E2%2B3x%2By-3%3D0%E5%BE%97x%5E2%2B3x%2Bk-x-3%3D0x%5E2%2B2x%2Bk-3%3D0%E4%BB%A4%E2%96%B3%3D4-4%28k-3%29%3D0%E8%A7%A3%E5%BE%97k%3D4%E6%95%85x%2By%E7%9A%84%E6%9C%80%E5%A4%A7%E5%80%BC%E4%B8%BA4%E8%BF%99%E9%87%8C%E4%B8%BA%E4%BD%95%E4%BB%A4%E2%96%B3%3D4-4%28k-3%29%3D0%3F)
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