#include <stdio.h>

void main(){
	double a[3], b[3];
	double x;

	a[0] = 1.2;
	a[1] = 3.4;
	a[2] = 5.6;
	b[0] = 7.8;
	b[1] = 9.1;
	b[2] = 2.3;

	/* calc */
	x = ここを記述！

	printf("A x B = %lf\n", x);
}