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1.
#include <stdio.h>

int main(){
	double beolvas,min,max,osszeg,atlag;
	int db;

	db=0;
	osszeg = 0.0;
	scanf("%lg",&beolvas);
	min = max = beolvas;
	while(beolvas!=0.0){
		osszeg += beolvas;
		db++;
		if(min>beolvas)min=beolvas;
		if(max<beolvas)max=beolvas;
		scanf("%lg",&beolvas);
	}

	if(db>0){
		atlag = osszeg / db;
		printf("A %d db valos szam atlaga %g, minimuma %g, maximuma %g.\n",
			db,atlag,min,max);
	}

	return 0;
}
==============================================================
2.
#include <stdio.h>
#include <math.h>

int main(){
	double elozo,x;

	elozo=x=0;
	do{
		elozo = x;
		x = log(2*x+3);
		//x = 0.5 * (exp(x) - 3.0);
	}
	while( fabs(elozo-x) > 0.00001);

	printf("%g\n",x);
	return 0;
}
==============================================================
3.
#include <stdio.h>
#define _USE_MATH_DEFINES
#include <math.h>

int main(void){ // nem lett alaposan letesztelve. jó-e?
    double x, y, x0, y0, alfa, alfarad, A, v0, t, D;
    
    printf("A= ");  scanf("%lg", &A);
    printf("x0=");  scanf("%lg", &x0);
    printf("y0=");  scanf("%lg", &y0);
    printf("v0=");  scanf("%lg", &v0);

    for (alfa = alfarad = 0; alfa < 90; alfa += 2, alfarad = alfa * M_PI / 180){
        int talalt = 0;

        t = (x0 - A / 2) / (v0 * cos(alfarad));
        y = v0 * t * sin(alfarad) - 9.81 / 2 * t * t;
        if (y >= y0 - A / 2 && y <= y0 + A / 2)
            talalt = 1;

        t = (x0 + A / 2) / (v0 * cos(alfarad));
        y = v0 * t * sin(alfarad) - 9.81 / 2 * t * t;
        if (y >= y0 - A / 2 && y <= y0 + A / 2)
            talalt = 1;

        D = v0*sin(alfarad);
        D *= D;
        D -= 2 * 9.81*(y0 - A / 2);
        if (D > 0){
            D = sqrt(D);
            x = (v0*sin(alfarad) + D) / 9.81;
            if (x >= x0 - A / 2 && x <= x0 + A / 2)
                talalt = 1;
            x = (v0*sin(alfarad) - D) / 9.81;
            if (x >= x0 - A / 2 && x <= x0 + A / 2)
                talalt = 1;
        }

        D = v0*sin(alfarad);
        D *= D;
        D -= 2 * 9.81*(y0 + A / 2);
        if (D > 0){
            D = sqrt(D);
            x = (v0*sin(alfarad) + D) / 9.81;
            if (x >= x0 - A / 2 && x <= x0 + A / 2)
                talalt = 1;
            x = (v0*sin(alfarad) - D) / 9.81;
            if (x >= x0 - A / 2 && x <= x0 + A / 2)
                talalt = 1;
        }

        if (talalt)
            printf("%g fok\n", alfa);
    }

    return 0;
}