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diff --git a/3760/CH5/EX5.56/Ex5_56.sce b/3760/CH5/EX5.56/Ex5_56.sce
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index 000000000..583f094a1
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+++ b/3760/CH5/EX5.56/Ex5_56.sce
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+clc;
+xd=1.2; // pu d-axis synchronous reactance
+xq=0.8; // pu q-axis synchronous reactance
+xe=0.1; // pu external reactance
+vb=1; // voltage of infinite bus
+pf=0.9; // lagging power factor
+disp('case a');
+// vb=vt-j*ia*xe -(1)where ia is armature current
+// ia=ia*(pf-%i*sqrt(1-pf^2)); // complex form of armature current
+// vt*ia=1 therefore ia=1/vt solving equation 1 we get a quadratic equation in vt whose terms are  
+t1=1; 
+t3=-2*xe*sqrt(1-pf^2)-vb;
+t5=(xe*sqrt(1-pf^2))^2-(pf*xe)^2; // terms of quadratic equation in terminal voltage
+p= [t1 0 t3 0 t5];
+vt=roots(p);
+ia=1/vt(2); // pu armature current
+printf('Generator terminal voltage is %f pu\n',vt(2));
+printf('Armature current is %f pu\n',ia);
+disp('case b');
+Ef=vt(2)+ia*(pf-%i*sqrt(1-pf^2))*%i*xq; 
+de=atand(imag(Ef),real(Ef));
+pa=acosd(pf); // power factor angle
+id=ia*sind(de+pa); // d-axis component of armature current
+Ef=abs(Ef)+id*(xd-xq);
+printf('Load angle is %f degrees\n',de);
+printf('Excitation voltage is %f pu',Ef);