4. Find z if: (a) $8z=53^{2}-452$ (b) $13z=782-26^{2}$ 5. If $3y$ $\dfrac {1} {3y}$ $7$ find $9y^{2}+\dfrac {1} {9y^{2}}$ 6. If $5y+\dfrac {1} {5y}=6$ 6 find $5y-\dfrac {1} {5y}$ 7. Simplify: (a) $\left(a^{2}-2b^{2}\right)^{2}$ (b) $\left(x+3y\right)^{2}-\left(x-3y\right)^{2}$ (c) $\left(5x+2y\right)^{2}+\left(5x-2y\right)^{2}$ (d) $\left(2x+3y\right)^{2}+\left(2x-3y\right)^{2}$ (c) $\left(1.1x-0.9y\right)^{2}-$ $-\left(0.9x-1.1y\right)^{2}$ $\left(2x$ $+5y^{2}\right)^{2}-20xy^{2}$ 8. Show $1ha1$ (a) $\left(2x-7y\right)^{2}+28xy=4x^{2}+49y^{2}$ (b) $\left(3xy-7yz\right)^{2}+84xy^{2}z=\left(3xy$ $+7yz\right)^{2}$ (c) $\left(4x+5y\right)^{2}-\left(4x-5y\right)^{2}=80xy$ (e) $\left(n-b\right)\left(a+b\right)+\left(b-c\right)\left(b+c\right)+\left(c-a\right)\left(c+a\right)=0$

Simplify: $1$ $2a+3b-a-2b$ b. $7x^{2}-5xy+2xy-5x^{2}$ C. $3a^{2}-2a+5a^{2}+7a$ $d$ $2xy+3y2-xy-2y2$ $20xyx+14yz-6xx+2xyz-12yz-3xx$

The sum of two algebrate expressions Is $3θa^{4}-22a^{3}b+27ab^{2}-b^{3}$ One of them $1$ 1s $13.$ $2b^{3}+17a^{4}$ $-13a^{3}b$ Find the other. $13$ Simplify the following. $11\right)$ $9a+3a-2a+11a$ $111\right)$ $5ab+6cd+11ab-12ab-3cd-ab+7cd$ $\left(111\right)$ $7+5a^{2}b-6ab^{2}+9+3ab^{2}-2a^{2}b-12+15ab^{2}$ $11y\right)$ $8a+3b-7c-7a+2b-3c+9c+11a-b$