2 + 2

Round[number,multiple]

Solve[(x^2)+ 8x - 9==0,x]

Solve[(x^2)-21Sin[x]+8x-9 ==0]

NSolve[-9+8 x+(x^2)-21 Sin[x]==0,x]

FindRoot[-9+8 x+(x^2)-21 Sin[x]==0,{x,1}]

Plot[-9+8 x+(x^2)-21 Sin[x],{x,4,5},AxesOrigin->{0,0}]

Plot[-9+8 x+(x^2)-21 Sin[x],{x,-20,20}]

Plot[-9+8 x+(x^2)-21 Sin[x],{x,-12,-5}]

FindRoot[-9+8 x+(x^2)-21 Sin[x]==0,{x,0}]

FindRoot[-9+8 x+(x^2)-21 Sin[x]==0,{x,2}]

Plot[-9+8 x+(x^2)-21 Sin[x],{x,2,3}]

f[x_]:=-9+8 x+(x^2)-21 Sin[x]

f[x]

f[t]

f[2]

f[2.0]

f[2.]

f[3]

f[3.0]

Plot[((-9+8 x+(x^2)-21 Sin[x])/((x^2)-4)),{x,-12,12}]

Plot[((-9+8 x+(x^2)-21 Sin[x])/((x^2)-4)),{x,2.01,5}]