1.
#include <stdio.h>
#include <math.h>

int main(){
	double a,b,c,diszkr,x1,x2;

	printf("a="); scanf("%lg",&a);
	printf("b="); scanf("%lg",&b);
	printf("c="); scanf("%lg",&c);

	if(a==0.0)
		printf("Linearis egyenlet, gyoke: %g\n",-c/b);
	else{
		diszkr = b*b - 4.0*a*c;
		if(diszkr < 0)
			printf("Nincs valos megoldas.\n");
		else if(diszkr == 0)
			printf("Egy gyok van: %g\n", -b/(2*a) );
		else{
			diszkr = sqrt(diszkr);
			x1 = ( -b + diszkr ) / (2*a);
			x2 = ( -b - diszkr ) / (2*a);
			printf("A gyokok:\n%g\n%g\n",x1,x2);
		}
	}
	return 0;
}

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2.
#include <stdio.h>
#define _USE_MATH_DEFINES
#include <math.h>

int main(){
	double a,b,c,T,alfa,beta;
	
	scanf("%lg%lg",&a,&b);
	
	c = sqrt(a*a+b*b);
	T = a*b/2.0;
	alfa = atan2(a,b);
	beta = M_PI / 2.0 - alfa; 

	printf("c=%g\nT=%g\nalfa=%g\nbeta=%g\n",
		c,T,alfa/M_PI*180,beta/M_PI*180);
	return 0;
}

==============================================================
3.
#include <stdio.h>
#include <math.h>

int main(){
	double a,b,c,min,max,x,dx,osszeg=0.0;

	printf("Az egyenlet együtthatoi (a,b,c): ");
	scanf("%lg%lg%lg",&a,&b,&c);
	printf("A tartomany hatarai (min,max): ");
	scanf("%lg%lg",&min,&max);

	dx = (max - min) / 10000.0;
	for( x = min; x < max; x += dx){
		double fx = a*x*x + b*x + c;
		osszeg += dx*fx;
	}
	printf("Az integral: %g\n",osszeg);
	return 0;
}