Question: properties of the ellipse

restart
EQ := proc(M, N) RETURN((y - M[2])/(x - M[1]) = (N[2] - M[2])/(N[1] - M[1])); end proc:
 with(plots):   
 with(geometry):   
_EnvHorizontalName := 'x':   _
EnvVerticalName := 'y':  
a := 7;  b := 5;  
c:=sqrt(a^2-b^2); 
 t:= (3* Pi)/(4):    
ellipse(el,x^2/a^2 + y^2/b^2 - 1 ): 
 point(M1, a*cos(t),b*sin(t)):  
point(F1,-c,0):point(F2,c,0):    
line( L1,[F1,M4]): 
point(M1, a*cos(t),b*sin(t)):  
EQ([a*cos(t),b*sin(t)],[-c,0]);  
solve(`%`,y);m:=coeff(`%`,x);   
line(L3,y=m*(x-c)); 
op(solve({x^2/a^2 + y^2/b^2 - 1 =0, y=m*(x-c)},{x,y},explicit)[2])[1]:xM2:=rhs(`%`):  
op(solve({x^2/a^2 + y^2/b^2 - 1 =0, y=m*(x-c)},{x,y},explicit)[2])[2]:yM2:=rhs(`%`):  
point(M2,xM2,yM2); 
line( tang1,x*xM2/a^2 + y*yM2/b^2 = 1);  
intersection(C1,L1,tang1);  
line(L4,[F1,M2]);  C1:=[ HorizontalCoord(C1), VerticalCoord(C1)]; 
 F1:=[-c,0];M2:= [ HorizontalCoord(M2), VerticalCoord(M2)];    
display( [ textplot( [[ -c, 0, "F1"],[ c,0, "F2"] ,                         
[ HorizontalCoord(M1), VerticalCoord(M1), "M1"],                          
[ HorizontalCoord(M2), VerticalCoord(M2), "M2"],                         
[ HorizontalCoord(C1), VerticalCoord(C1), "C1"] ],'align'={"above",'right'},                       [polygonplot([C1,F1,M2], color=blue,filled=true,transparency=0.9)]);     
draw( [ el(color=red),M1(color=black,symbol=solidcircle, symbolsize=16),
                      M2(color=black,symbol=solidcircle, symbolsize=16),                      
                      L1( color=black),L3(color=green),L4(color=green),                      
                      tang1(color=red), 
                      F1(color=blue, symbol=solidcircle, symbolsize=16),                      
                      F2(color=red, symbol=solidcircle, symbolsize=16),
                      C1(color=black, symbol=solidcircle, symbolsize=16),                     ],                                    axes=none ) ] );
Error, missing operator or `;` Many errors Icant corrected.  Thank you.