使沉在水里的物体浮起来

因式分解x的2次方+(p+q)x+pq型方程怎么算打个比方x的2次方+(p+q)x+pq解例如：a^2+2a-8这个式子用x的2次方+（p+q)x+pq麻烦写详细点, 计算（2x^3-3x^y-2xy^2）-（x^3-2xy^2+y^3）+（-x^3+3x^2y-y^3）的值 其中x=1/2,y=-1 将x错抄成-1/2计算结果却和正确答案一样 请解释原因 x²+（p+q）x+pq型式子的因式分解 数学三角函数化简题18.化简sin(π-α)sin([π/2]-α)/cos(π+α)cos([π/2]+α);(2)若tanα=2求 [sinα+cosα]/[（sinα-cosα）+cos^2α]之值19.已知tan(α+β)=3,tan(α-β)=5,求tan2α,tan2β的值 1.cosx/(1+sinx)=(1-sinx)/cosx=(cosx+1-sinx)/(1+sinx+cosx)2.sinx/(1+cosx)=(1-cosx)/sinx=(sinx+1-cosx)/(1+sinx+cosx)请问.第一个式子cosx/(1+sinx)怎么化到第二个式子、第三个式子的?就是为什么相等?第一个式子基本看懂了 三角函数式的化简（1+sina+cosa)(sina/2-cosa/2)/根号下2+2cosa （0 数学三角函数化简 三角函数式的化简cotα+sinα/（1+cosα）= If you go _____ (shop)this afternoon. Where were you this afternoon? I (wondered) if you were free this afternoon括号了为什么填的是wondered而不是wonder?时间不是this afternoon吗？怎么会是过去式？ I ____this afternoon,but you were out.空格处为何用did call而不用have called? The students were at school (yesterday afternoon)对括号里的提问 Were you hunry after school yesterday afternoon?（were是are过去式）怎么做肯定回答 .yes,后面是什么.i were么 看 着好别扭. 英语翻译还有 Did you was TV yesterday 计算-2^2010+2^2011应等于（ ） A 、-2^2010 B、-2^2011 C、-1 D、2^2010 I was at school at three yesterday afternoon.对at school 划线部分提问 求x²-(p²+q²)x+pq(p+q)(p-q)和x²-2xy-8y²-x-14y-6因式分解 计算|3分之1-2分之一|4分之一-3分之1|+|5分之一-4分之一|+.+|2012分之一-2011分之一|怎么算 They were visiting the history museum at one o'clock yesterday afternoon .（对划线部分提问）划线部分：visiting the history museum ______ ______ they ______ at one o'clock yesterday afternoon 如果（x²+ax+8)(x²-3x+b)的展开式中不含有x³项且常数项为1,求a的-b次方+b的-a次方= 根号2分之[根号32-根号8] 根号32-根号8分之9+根号2分之25 根号32-根号8+2根号2分之一2x²-4x-1=0 要使（AX²-3X）（X²-2X+1）的之中不含X³项,则A= We were ( ) bookshop yesterday afternoon while we were walking yesterday afternoon.the bell rang. What were you doing yesterday afternoon?— We were singing ____.A.all the time B.always C.on tA all the time B always C on time D in time 2分之 9 正负根号73 等于多少 若-2x²*(3x-ax-6)-3x³+x²的结果中不含x³项,则a的值是 已知(x²+ax+8)(x²-3x+b)中不含x³项和x项,则a,b的值分别为多少? 2(ax²—x³）+b(x²+ax)=ax³—3x²－cx 求a+b+c的值