问答题设，求B-1．
问答题设函数z=f(x，y)定义在整个二维平面域R2，满足下列条件：①(x，y)∈R2，f(x，y)≥0，当且仅当(x，y)=(0，0)时，f(x，y)=0；②(x，y)∈R2，λ∈R，f(λx，λy)=|λ|f(x，y)；③(x，y)，(u，v)∈R2，f(x+u，y+v)≤f(x，y)+f(u，v)．证明下列命题成立：
问答题已知f(x1，x2，x3，x4)=x1x2+x2x3+x3x4+x4x1，用配方法化二次型为标准形式，并求所作可逆线性变换及二次型的秩和正、负惯性指数．
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问答题设线性方程组①与方程组x1+x2+x3=a-1②有公共解，求a的值及所有公共解．
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问答题Directions: You got sick just two weeks before the final examination and were sent to hospital. One doctor treated you very well and you recovered soon. Write a letter of appreciation to the doctor (Ms. Green). You should write about 100 words on ANSWER SHEET 2. Do not sign your own name at the end of the letter. Use "Li Ming" instead. Do not write the address. (10 points)
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问答题设z=f(2z-y，ysinx)，其中f(u，v)具有连续的二阶偏导数，求
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问答题设u=f(x，y，z)，其中．其中厂有二阶连续偏导数．
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问答题二次型，经正交变换化为+(1)求a，t的值；(2)求所用的正交变换．
问答题一个半球体状的雪堆，其体积融化的速率与半球面面积S成正比，比例常数K＞0．假设在融化过程中雪堆始终保持半球体状，已知半径为r0的雪堆在开始融化的3个小时内，融化了其体积的，问雪堆全部融化需要多少小时?
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