I have a problem with the angle output of mpu6050 sensor.

Question

Hello

I am working on mpu6050 sensor in sdk v14.
I succeeded in obtaining the acceleration value of this. I'm trying to get the angle of the sensor using this value.

I searched the Internet and used a formula to obtain angles using acceleration values. However, as shown in the picture below, the value of the angle is only zero.

This is my main.c code.

#include <stdbool.h>
#include <stdint.h>
#include <string.h>

#include "nordic_common.h"
#include "nrf.h"
#include "app_error.h"
#include "app_timer.h"
#include "nrf_delay.h"

#include "app_mpu.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"


volatile bool start_accel_update_flag = false;




void timer_accel_update_handler(void * p_context)
{
    start_accel_update_flag = true;
}


/**@brief Function for initializing the nrf log module.
 */
static void log_init(void)
{
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}


void mpu_init(void)
{
    ret_code_t ret_code;
    // Initiate MPU driver
    ret_code = app_mpu_init();
    APP_ERROR_CHECK(ret_code); // Check for errors in return value
    
    // Setup and configure the MPU with intial values
    app_mpu_config_t p_mpu_config = MPU_DEFAULT_CONFIG(); // Load default values
    p_mpu_config.smplrt_div = 19;   // Change sampelrate. Sample Rate = Gyroscope Output Rate / (1 + SMPLRT_DIV). 19 gives a sample rate of 50Hz
    p_mpu_config.accel_config.afs_sel = AFS_2G; // Set accelerometer full scale range to 2G
    p_mpu_config.gyro_config.fs_sel = AFS_2G;
    ret_code = app_mpu_config(&p_mpu_config); // Configure the MPU with above values
    APP_ERROR_CHECK(ret_code); // Check for errors in return value 
}


/**@brief Function for application main entry.
 */
int main(void)
{
    uint32_t err_code;
    bool erase_bonds;

    // Initialize.
    log_init();
    NRF_LOG_INFO("\033[2J\033[;H"); // Clear screen

    mpu_init();
    
    // Start execution.
    NRF_LOG_INFO("MPU simple example.");


    accel_values_t accel_values;
    gyro_values_t gyro_values;
        
    // Enter main loop.
    for (;;)
    {
        if (NRF_LOG_PROCESS() == false)
        {
            app_mpu_read_accel(&accel_values);
            app_mpu_read_gyro(&gyro_values);
            
            err_code = app_mpu_read_accel(&accel_values);
            APP_ERROR_CHECK(err_code);
            err_code = app_mpu_read_accel(&gyro_values);
            APP_ERROR_CHECK(err_code);

            //float accel_x = accel_values.x * 4.0 / 32768.0; //same nano33ble lsm9ds1 sensor value
            //float accel_y = accel_values.y * 4.0 / 32768.0;
            //float accel_z = accel_values.z * 4.0 / 32768.0;

            float accel_x = accel_values.x;
            float accel_y = accel_values.y;
            float accel_z = accel_values.z;

            //Angle formula
            float RADIAN_TO_DEGREES = 180/3.14139;
            float val_x = atan(accel_y/sqrt(pow(accel_x,2) + pow(accel_z,2))) * RADIAN_TO_DEGREES; //X slope
            float val_y = atan(accel_x/sqrt(pow(accel_y,2) + pow(accel_z,2))) * RADIAN_TO_DEGREES; //Y slope


            //Accel value
            NRF_LOG_INFO("Accel_X : "NRF_LOG_FLOAT_MARKER"", NRF_LOG_FLOAT(accel_x)); //float print
            NRF_LOG_INFO("Accel_Y : "NRF_LOG_FLOAT_MARKER"", NRF_LOG_FLOAT(accel_y));
            NRF_LOG_INFO("Accel_Z : "NRF_LOG_FLOAT_MARKER"", NRF_LOG_FLOAT(accel_z));

            //Angle value
            NRF_LOG_INFO("X-Angle : "NRF_LOG_FLOAT_MARKER"", NRF_LOG_FLOAT(val_x)); //float print
            NRF_LOG_INFO("Y-Angle : "NRF_LOG_FLOAT_MARKER"", NRF_LOG_FLOAT(val_y));

            nrf_delay_ms(1000);

            start_accel_update_flag = false;
        }
   }
}

I tried debugging, but I couldn't find the cause of the problem.
Can I know the problem with this?

Thank you.