已知抛物线y=ax2+bx+c过点（1，1），且在点（2，-1）处与直线y=x-3相切，求a、b、c的值。
解：∵y=ax2+bx+c过点（1，1），
∴a+b+c=1，
∵y′=2ax+b，
∴曲线过点P（2，-1）的切线的斜率为4a+b =1，
又曲线过点（2，-1），
∴4a+2b+c=-1，
由
解得
∴a、b、c的值分别为3、-11、9。
My favorite animals are elephants. Elephants are 1 living animals on land. There are two kinds of elephants--African elephants and 2 elephants. African elephants are larger than Indian elephants, and they have 3 ears. Elephants have to eat 4 because they are so big. One elephant can eat between 100 5 1,000 pounds 6 grass in a day! They can live for 60--70 years. There are no bones in the back of 7 feet, only fat. Elephants walk on tiptoe. They can move quietly and walk in the mud 8. Elephants grow tusks. The tusks are large teeth that stick out of ___9__ mouths. Sometimes, hunters kill elephants 10 the tusks. People use the tusks to make beautiful things and piano keys.
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