a) \(\left(3x-5\right)\left(5-3x\right)+9\left(x+1\right)^2=30\)

\(\Rightarrow15x-9x^2-25+15x+9\left(x^2+2x+1\right)-30=0\)

\(\Rightarrow30x-9x^2-25+9x^2+18x+9-30=0\)

\(\Rightarrow48x-46=0\)

\(\Rightarrow x=\frac{23}{24}\)

b) \(\left(x+4\right)^2-\left(x+1\right)\left(x-1\right)=16\)

\(\Rightarrow\left(x^2+8x+16\right)-\left(x^2-1\right)=16\)

\(\Rightarrow x^2+8x+16-x^2+1=16\)

\(\Rightarrow8x+17=16\)

\(\Rightarrow8x=-1\)

\(\Rightarrow x=\frac{-1}{8}\)

c) \(\left(y-2\right)^3-\left(y-3\right)\left(y^2+3y+9\right)+6\left(y+1\right)^2=49\)

\(\Rightarrow\left(y-2\right)^3-\left(y^3-3^3\right)+6\left(y^2+2y+1\right)=49\)

\(\Rightarrow y^3-6y^2+12y-8-y^3+27+6y^2+12y+6=49\)

\(\Rightarrow\left(y^3-y^3\right)+\left(-6y^2+6y^2\right)+\left(12y+12y\right)+\left(-8+27+6\right)=49\)

\(\Rightarrow24y+25=49\)

\(\Rightarrow24y=24\)

\(\Rightarrow y=1\)

d) \(\left(y+3\right)^3-\left(y+1\right)^3=56\)

\(\Rightarrow\left(y+3-y-1\right)[\left(y+3\right)^2+\left(y+3\right)\left(y+1\right)+\left(y+1\right)^2]=56\)

\(\Rightarrow2\left(y^2+6y+9+y^2+4y+3+y^2+2y+1\right)=56\)

\(\Rightarrow3y^2+12y+13=28\)

\(\Rightarrow\left(3y^2+15y\right)-\left(3y+15\right)=0\)

\(\Rightarrow3y\left(y+5\right)-3\left(y+5\right)=0\)

\(\Rightarrow3\left(y-1\right)\left(y+5\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-1=0\\x+5=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=1\\x=-5\end{cases}}\)

A = 2(x³ + y³) - 3(x² + y²) + 30

= 2(x + y)(x² - xy + y²) - 3(x² + 2xy + y² - 2xy) + 30

= 2 (1)(x² + 2xy + y² - 3xy) - 3( (x + y)² - 2xy ) + 30

= 2( (x + y)² - 3xy ) - 3( (1)² - 2xy ) + 30

= 2( 1² - 3xy ) - 3 ( -2xy ) + 30

= 2( 1 -3xy ) - 3 ( 1 -2xy ) + 30

= 2 - 6xy -3 + 6xy + 30

= -1 + 30

= 29

Vậy A = 29 khi x + y = 1

tìm y1 )15 + y + 3 x 6 : 2 = 302 ) 15 + { y +3 } x 6 : 2 = 30

mình chỉ biết câu 1 chứ mình không biết câu 2 

đáp án của mình là 2 ,mà mình không chắc cho lắm